Stress compensated piezoelectric crystal device

Abstract

A stress compensated quartz piezoelectric resonator disk. The resonator contains a thin resonant center disk and a thicker integral concentric peripheral support ring. Roughly pie-slice portions of the inner disk are cut away. The remaining bridges between the resonant disk and support ring are positioned and sized in accord with crystallographic theory so that forces applied to the support ring will not change the resonant frequency of the disk.

What is claimed is: 
     
       1. A piezoelectric crystal comprising: a piezoelectric resonant plate having a periphery and having a crystallographic force-frequency function, said crystallographic force-frequency function being zero for at least one null point on said periphery and the mathematical integral of said periphery being non-zero;   a supporting member positioned adjacent to but spaced separately from said plate; and   at least one supporting bridge coplanar with said plate and connected to a first position of said periphery, said first portion including at least one said null point, the angular span of said bridge being asymmetrically positioned about said null point and the mathematical integral of said crystallographic force-frequency function over said first portion being zero; and   at least one second portion of said periphery hanging free.   
     
     
       2. A piezoelectric crystal comprising: an AT-cut quartz resonant disk of diameter greater than fifteen times its thickness, said disk having a crystal X-axis in the plane of said disk;   a thicker concentric support ring; and   two bridges coplanar and integral with and connected between the periphery of said resonant disk and said support ring, said bridges being positioned with respect to said crystal X-axis to span the angular ranges 40.4° to 139.6° and 220.4° to 319.6°, the remainder of said periphery of said disk hanging free.   
     
     
       3. A piezoelectric crystal comprising: an SC-cut quartz resonant disk of diameter greater than fifteen times its thickness, said disk having a crystal X-axis in the plane of said disk;   a thicker concentric support ring; and   four bridges coplanar and integral with and connected between the periphery of said resonant disk and said support ring, said bridges being positioned with respect to said crystal X-axis to span the angular ranges 66.35° to 97.40°, 160.68° to 180.28°, 246.35° to 277.40°, and 340.68° to 360.28°, the remainder of said periphery of said disk hanging free.